Laptop stops stream to VGA monitor when windows starts.

Maybe your screen resolution is too high for your external monitor. To fix this, you can boot in VGA mode in Vista. To do so, press F8 just before the Windows loading screen appears. You can press F8 repeatedly to make sure you get the timing right. A menu will appear and you can choose to boot in VGA mode. If it works, try to lower the resolution to something like 1024x768.

If it's not working, try to change the dual-screen option of your laptop. It depends on the brand, but it's usally something like Function+F4. Do it 2-3 times in a row to cycle through the modes and see if ones actually works.

If all of the above fails, I don't know what else could works. Good luck!

This sounds like the problem. When windows boots, it loads your graphics driver and disables the display. Changing the output to the primary one should solve your issue.